Voltage-controlled variable frequency oscillation circuit and signal processing circuit

ABSTRACT

A voltage-controlled variable frequency oscillation circuit, includes: an oscillation circuit section including a resonance circuit which includes a coil and a variable capacitance element, and a negative resistance circuit; and a first resistor connected between the oscillation circuit section and a first one of a pair of terminals of a power supply.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent ApplicationJP 2008-097064, filed in the Japan Patent Office on Apr. 3, 2008, theentire contents of which is being incorporated herein by reference.

BACKGROUND

The present application relates to a voltage-controlled variablefrequency oscillation circuit and a signal processing circuit which usesan oscillation frequency signal from a voltage-controlled variablefrequency oscillation circuit to carry out a predetermined signalprocess.

As a voltage-controlled variable frequency oscillation circuit(hereinafter referred to sometimes as VCO (Voltage ControlledOscillator)), a VCO of the LC resonance type wherein a coil and avariable capacitance element are used for a resonance circuit is usedpopularly.

An example of a conventional VCO of the LC resonance type is shown inFIG. 14. Referring to FIG. 14, the VCO shown includes an oscillationcircuit section 103 which includes a resonance circuit 101 and anegative resistance circuit 102. The oscillation circuit section 103 isdirectly connected to a power supply line 104 to which a power supplypotential VDD is supplied, and the negative resistance circuit 102 isbiased by a current source 105.

The resonance circuit 101 includes a pair of coils L1 and L2 and avariable capacitance circuit 110. The variable capacitance circuit 110in the configuration shown in FIG. 14 includes two varactors 111 and 112as variable capacitance elements.

As a varactor which can be used for the varactors 111 and 112, varactorsof various configurations are available, and at least two differentconfigurations of varactors are available. A varactor of one of theconfigurations is shown in FIG. 15A.

Referring to FIG. 15A, each of the varactors 111 and 112 is formed froma MOSFET (Metal Oxide Semiconductor Field Effect Transistor) 106 whosesource and drain are connected to each other. As shown in FIG. 15A, aterminal 106 a is led out from a connecting point of the source and thedrain of the MOSFET 106, and the other terminal 106 b is led out fromthe gate of the MOSFET 106.

Another example of a configuration of a varactor uses a MOS structurewhich uses the gate terminal and the well terminal.

Although any of the varactors can be used for the LC resonance circuit,it is assumed that, in the following description, a varactor of theconfiguration described above with reference to FIG. 15A is used for theconvenience of description.

If a controlling voltage VG is applied between the terminals 106 a and106 b, then the varactor exhibits a capacitance value C in accordancewith the controlling voltage VG as seen in FIG. 15B. Accordingly, thecapacitance value C can be varied by varying the controlling voltage VG,and the VCO varies the oscillation output frequency thereof in responseto the variation of the capacitance value C.

In the variable capacitance circuit 110 of FIG. 14, the varactors 111and 112 are connected at one terminal thereof, that is, at the terminal106 a side thereof, to each other, and a controlling voltage VC isconnected to a connecting point P0 between them. The varactor 111 isconnected at the opposite terminal thereof, that is, at the terminal 106b thereof, to the power supply line 104 through the coil L1, and theother varactor 112 is connected at the opposite terminal thereof, thatis, at the terminal 106 b thereof, to the power supply line 104 throughthe coil L2.

The negative resistance circuit 102 in FIG. 14 is formed from adifferential circuit of a pair of MOSFETs 121 and 122. In particular,the MOSFETs 121 and 122 are connected at the source thereof to eachother, and the connecting point between them is grounded through thecurrent source 105. Further, the drain of the MOSFET 121 and the gate ofthe MOSFET 122 are connected to each other, and the connecting pointbetween them is connected to a connecting point P1 between the coil L1and the varactor 111. Furthermore, the drain of the MOSFET 122 and thegate of the MOSFET 121 are connected to each other, and the connectingpoint between them is connected to a connecting point P2 between thecoil L2 and the varactor 112.

In the VCO of FIG. 14, the oscillation circuit section 103 is connecteddirectly to the power supply line 104 to which the power supplypotential VDD is supplied. Therefore, the dc (direct-current) potentialdifference between the opposite terminals of the variable capacitancecircuit 110, that is, between the connecting points P1 and P2, issubstantially equal to the power supply potential VDD, and thecapacitance variation region by the varactors 111 and 112 cannot be usedeffectively. As a result, there is a problem that the frequencyvariation region of the VCO cannot be increased.

A case is studied here wherein, in FIG. 15A, the potential at theterminal 106 a is represented by Va and the potential at the terminal106 b is represented by Vb, and the potential Va is varied withreference to the potential Vb to vary the controlling voltage VG. Inthis instance, if the value of the potential Va is varied within therange of Vb−α<Va<Vb+α, then the controlling voltage VG assumes a valuewhich satisfies −α<VG<α as seen in FIG. 15B, and the capacitance value Cexhibits an optimum variation range W0.

However, in the case of the VCO of FIG. 14, the potential at theopposite terminal side, that is, at the terminal 106 b side, of thevaractors 111 and 112, is the power supply potential VDD. Therefore,even if it is tried to use the controlling voltage VC to vary thepotential on the first terminal side, that is, at the terminal 106 aside, of the varactors 111 and 112, the controlling voltage VC cannot bemade equal to or higher than the power supply potential VDD readily froma restriction of a driving circuit. The variation characteristic of thecapacitance value C of the varactor with respect to the controllingvoltage VC at this time is such as indicated by a solid line curve 201of FIG. 16. As a result, there is a problem that the variation range ofthe capacitance value C of the variable capacitance circuit 110 becomesa variation range W1 very narrower than the optimum variation range W0(refer to FIG. 15B) as seen in FIG. 16.

Against this problem, it is proposed in Japanese Patent Laid-Open No.2004-147310 (hereinafter referred to as Patent Document 1) to use such aconfiguration as shown in FIG. 17 for the variable capacitance circuit110 described above to increase the variation range of the capacitancevalue C of the variable capacitance circuit 110.

Referring to FIG. 17, a dc cutting capacitor 113 is connected betweenthe varactor 111 and the connecting point P1 while another dc cuttingcapacitor 114 is connected between the varactor 112 and the connectingpoint P2. A connecting point between the varactor 111 and the capacitor113 is connected to a dc bias potential VBIAS through a resistor 115while a connecting point between the varactor 112 and the capacitor 114is connected to the dc bias potential VBIAS through another resistor116.

According to the configuration shown in FIG. 17, a bias voltage issupplied to the second terminal side, that is, to the terminal 106 bside, of the varactors 111 and 112 through the resistors 115 and 116,respectively. Accordingly, the potential at the second terminal side,that is, at the terminal 106 b side, of the varactor 111 and thevaractor 112 becomes lower than the power supply potential VDD and canbe reduced ideally to VDD/2.

Accordingly, the variation characteristic of the capacitance value C ofthe varactors 111 and 112 with respect to the controlling voltage VCwhen the controlling voltage VC supplied to the connecting point P0 ofthe varactors 111 and 112 is varied up to the power supply potential VDDbecomes such as indicated by a solid line curve 202 in FIG. 16. As aresult, the variation range of the capacitance value C of the variablecapacitance circuit 110 becomes a wider variation range W2 as seen inFIG. 16, and a wider frequency range than that of the example of FIG. 14can be achieved with the VCO.

SUMMARY

However, where the variable capacitance circuit 110 shown in FIG. 17 isused, the capacitors 113 and 114 are connected in series to thevaractors 111 and 112, respectively. Therefore, the capacitancevariation region of the variable capacitance circuit effectivelydecreases by an amount provided by the series connected capacitors 113and 114.

As a result, the voltage-controlled oscillator of the configurationdisclosed in Patent Document 1 suffers from a new problem that a widefrequency variation region corresponding to the capacitance variationregion of a variable capacitance element cannot be assured.

Therefore, it is desirable to provide a voltage-controlled variablefrequency oscillation circuit with which a wide frequency variationregion in accordance with a capacitance variation region of a variablecapacitance element can be assured.

According to an embodiment, there is provided a voltage-controlledvariable frequency oscillation circuit including an oscillation circuitsection including a resonance circuit which includes a coil and avariable capacitance element, and a negative resistance circuit, and afirst resistor connected between the oscillation circuit section and afirst one of a pair of terminals of a power supply.

In the voltage-controlled variable frequency oscillation circuit, sincethe first resistor is connected between the oscillation circuit sectionand the first one of the terminals of the power supply, the power supplypotential is applied to the variable capacitance element of theresonance circuit through the first resistor. Meanwhile, a voltage lowerthan the power supply voltage is applied to one terminal of the variablecapacitance element of the resonance circuit.

Accordingly, the capacitance of the variable capacitance element whichis varied by the controlling voltage supplied to the second terminal ofthe variable resistance element varies over a variation range greaterthan that of the existing voltage-controlled variable frequencyoscillation circuit described hereinabove with reference to FIG. 14.

Further, in the voltage-controlled variable frequency oscillationcircuit of the present embodiment, since such a series capacitanceelement as in the existing voltage-controlled variable frequencyoscillation circuit is not provided for the variable capacitanceelement, the capacitance variation region by the variable capacitanceelement corresponds as it is to the variation region of the oscillationfrequency. Consequently, a frequency variation region greater than thatin the voltage-controlled variable frequency oscillation circuitdescribed hereinabove with reference to FIG. 17 can be assured.

In summary, with the voltage-controlled variable frequency oscillationcircuit, since the capacitance variation range of the variablecapacitance circuit corresponds directly to the variable capacitanceregion of the variable capacitance element, a greater frequencyvariation region can be assured.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a circuit diagram showing a voltage-controlled variablefrequency oscillation circuit according to a first embodiment;

FIG. 2 is a diagram illustrating a control characteristic of thevoltage-controlled variable frequency oscillation circuit of FIG. 1;

FIG. 3 is a circuit diagram showing a voltage-controlled variablefrequency oscillation circuit according to a second embodiment;

FIG. 4 is a connection diagram showing a particular example of aconfiguration of part of the voltage-controlled variable frequencyoscillation circuit of FIG. 3;

FIG. 5 is a diagram illustrating operation of a voltage-controlledvariable frequency oscillation circuit according to a third embodiment;

FIG. 6 is a circuit diagram showing the voltage-controlled variablefrequency oscillation circuit according to the third embodiment;

FIG. 7 is a block diagram showing an example of a processing circuit towhich the voltage-controlled variable frequency oscillation circuit ofFIG. 6 is applied;

FIG. 8 is a block diagram showing an example of a particularconfiguration of the processing circuit shown in FIG. 7;

FIG. 9 is a block diagram showing a particular configuration of part ofthe voltage-controlled variable frequency oscillation circuit shown inFIG. 8;

FIGS. 10 to 13 are circuit diagrams showing voltage-controlled variablefrequency oscillation circuits according to fifth to eighth embodiments,respectively;

FIG. 14 is a circuit diagram showing an example of a circuitconfiguration of an existing voltage-controlled variable frequencyoscillation circuit;

FIG. 15A is a schematic view showing a varactor as a variablecapacitance element used in the voltage-controlled variable frequencyoscillation circuit shown in FIG. 14 and FIG. 15B is a diagramillustrating a characteristic of the varactor of FIG. 15A;

FIG. 16 is a diagram illustrating a characteristic of the existingvoltage-controlled variable frequency oscillation circuit shown in FIG.14; and

FIG. 17 is a circuit diagram showing an example of a circuitconfiguration of part of an improved existing voltage-controlledvariable frequency oscillation circuit.

DETAILED DESCRIPTION

In the following, several voltage-controlled variable frequencyoscillation circuits (VCOs) according to different embodiments aredescribed with reference to the accompanying drawings. Incidentally, inthe figures used for illustrating following embodiments, for simplerdescription, the same components with those of the VCO shown in FIG. 14have the same numbers or symbols so as to omit their explanation.

First Embodiment

FIG. 1 shows a VCO according to a first embodiment.

Referring to FIG. 1, the VCO shown includes a first resistor 301 betweenan oscillation circuit section 103 and a power supply line from which apower supply potential VDD is obtained. In particular, in the VCO shownin FIG. 1, the first resistor 301 is connected between a connectingpoint P3 (potential VB) of a coil L1 and another coil L2 and a powersupply line 104 connected to a first terminal or a second terminal of apower supply.

A second resistor 302 is provided between the oscillation circuitsection 103 and a ground potential terminal which is the second terminalor the first terminal of the power supply. In other words, in the VCO ofFIG. 1, the second resistor 302 is connected between the connectingpoint of the sources of the MOSFETs 121 and 122 and the ground terminal.

In the configuration of the VCO of the first embodiment shown in FIG. 1,a bias voltage is applied to the connecting points P1 and P2 which arethe second terminal side, that is, the terminal 106 b side, of thevaractors 111 and 112 through the first resistor 301. Accordingly, thepotential (substantially equal to the potential VB at the connectingpoint P3) on the second terminal side, that is, on the terminal 106 bside, of the varactors 111 and 112 is lower than the power supplypotential VDD.

Particularly in the VCO of the first embodiment, the bias voltage forthe variable capacitance circuit 110 supplied to the connecting pointsP1 and P2 depends upon the resistance value of the first resistor 301and the resistance value of the second resistor 302. Thus, byappropriately setting the resistance value of the first and secondresistors 301 and 302, the bias voltage of the variable capacitancecircuit 110 can be set to VDD/2 or a value proximate to VDD/2.

Accordingly, the variation characteristic of the capacitance value C ofthe varactors 111 and 112 with respect to the controlling voltage VCsupplied to the connecting point P0 of the varactors 111 and 112 whenthe controlling voltage VC is varied up to the power supply potentialVDD can be made a maximum range as indicated by a solid line curve 203in FIG. 2. Since the variation range of the capacitance value C of thevariable capacitance circuit 110 conforms to the capacitance variationrange of the varactors 111 and 112, also this variation range increases.As a result, the frequency variation region of the VCO of the presentembodiment can be set to a variation range W3 proximate to the optimumvariation range W0.

Further, in the existing VCO described hereinabove with reference toFIG. 14, since the current source is formed from a MOS transistor,flicker noise in low frequencies is very high and this deteriorates thephase noise characteristic of the oscillation frequency of the VCOsignificantly. In contrast, with the VCO of the present embodiment,since the second resistor 302 is connected in place of the currentsource, the phase noise characteristic is improved.

Second Embodiment

In the VCO of the LC resonance type, the capacitance of the variablecapacitance circuit 110 is varied to vary the oscillation frequency ofthe VCO as described above. However, the resonance impedance of theresonance circuit 101 fluctuates in response to the variation of theoscillation frequency. Therefore, particularly in a low frequencyregion, the oscillation frequency of the oscillation output signal fromthe VCO drops, and the phase noise characteristic is deteriorated.

The VCO of the second embodiment is configured so as to solve theproblem of the deterioration of the phase noise characteristic. Anexample of a configuration of the VCO of the second embodiment is shownin FIG. 3.

Referring to FIG. 3, the VCO of the second embodiment is a modificationto but is different from the VCO of the first embodiment in that avariable resistance circuit 400 is provided in place of the firstresistor 301, and another variable resistance circuit 500 is provided inplace of the second resistor 302. Further, controlling signals VR1 andVR2 corresponding to a controlling voltage VC for the variablecapacitance circuit 110 are supplied from a controlling signalgeneration section 700 as resistance value controlling signals to thevariable resistance circuits 400 and 500, respectively. The othercomponents are configured similar to those of the VCO of the firstembodiment described.

In the VCO of the second embodiment, when the oscillation frequency ofthe VCO varies in response to the controlling voltage VC, thecontrolling signal generation section 700 controls the resistance valueof the variable resistance circuits 400 and 500 in response to thevariation of the oscillation frequency. In this configuration, a biascurrent value to the variable capacitance circuit 110 in response to theoscillation frequency of the VCO is controlled, whereby the oscillationamplitude of the oscillation output signal of the VCO is prevented fromdeteriorating.

Accordingly, in the VCO of the second embodiment, deterioration of thephase noise characteristic by variation of the oscillation frequency ofthe VCO can be prevented.

The variable resistance circuits 400 and 500 can be formed, for example,from a variable resistance element for which a MOSFET is used or from acombination of a resistance element and a switch circuit. Also it ispossible to use, for example, both of a variable resistance element forwhich a MOSFET is used and a combination of a resistance element and aswitch circuit.

FIG. 4 shows an example of a VCO wherein the variable resistancecircuits 400 and 500 are formed from a combination of a resistanceelement and a switch circuit.

Referring to FIG. 4, the variable resistance circuit 400 includes aplurality of MOSFETs 411, 412, . . . , 41 n (n is an integer equal to orgreater than 2: this similarly applies to the following description)serving as a switch circuit and resistors 421, 422, . . . , 42 nconnected in series to the MOSFETs 411, 412, . . . , 41 n, respectively.The series connections of the MOSFETs 411, 412, . . . , 41 n and theresistors 421, 422, . . . , 42 n are connected in parallel between theconnecting point P3 and the power supply line 104.

The controlling signal generation section 700 supplies an on/offswitching control signal to be supplied to the gate of the MOSFETs 411,412, . . . , 41 n as the controlling signal VR1 for resistance valuecontrol to the variable resistance circuit 400.

Similarly, the variable resistance circuit 500 includes a plurality ofMOSFETs 511, 512, . . . , 51 n serving as a switch circuit and resistors521, 522, . . . , 52 n connected in series to the MOSFETs 511, 512, . .. , 51 n, respectively. The series connections of the MOSFETs 511, 512,. . . , 51 n and the resistors 521, 522, . . . , 52 n are connected inparallel between the connecting point of the sources of the MOSFETs 121and 122 of the negative resistance circuit 102 and the ground terminal.

The controlling signal generation section 700 supplies an on/offswitching control signal to be supplied to the gate of the MOSFETs 511,512, . . . , 51 n as the controlling signal VR2 for resistance valuecontrol to the variable resistance circuit 500.

In the variable resistance circuit 400, the resistors connected inseries to those ones of the MOSFETs 411, 412, . . . , 41 n which arecontrolled to an on state are connected in parallel between theconnecting point P3 and the power supply line. Accordingly, the numberof resistors which are to be connected in parallel is varied by on/offcontrol of the MOSFETs 411, 412, . . . , 41 n and the resistance valueof the entire variable resistance circuit 400 is varied thereby.

Similarly, in the variable resistance circuit 500, the resistorsconnected in series to those ones of the MOSFETs 511, 512, . . . , 51 nwhich are controlled to an on state are connected in parallel betweenthe negative resistance circuit and the ground terminal. Accordingly,the number of resistors which are to be connected in parallel is variedby on/off control of the MOSFETs 511, 512, . . . , 51 n and theresistance value of the entire variable resistance circuit 500 is variedthereby.

Third Embodiment

In order to increase the frequency variation region of a VCO, frequentlya countermeasure is taken wherein the oscillation center frequency ofthe VCO is shifted as seen from characteristic curves 701, 702 and 703of FIG. 5. Also in this instance, it is necessary to take care so that,also in the shifted variable frequency range, the oscillation amplitudeof the oscillation output signal from the VCO may not deteriorate.

Also in this instance, the resistance value of the variable resistancecircuits 400 and 500 can be controlled to control the bias current valueto the variable capacitance circuit 110 in response to the oscillationfrequency of the VCO to prevent the oscillation amplitude of theoscillation output signal of the VCO from deteriorating.

The VCO according to the third embodiment is formed taking the foregoinginto consideration, and an example of a configuration of the VCO of thethird embodiment is shown in FIG. 6.

In the VCO of the third embodiment, the resonance circuit 101 includes acapacitance changeover circuit 600 connected in parallel to the variablecapacitance circuit 110 between the variable capacitance circuit 110 andthe coils L1 and L2 for shifting the oscillation center frequency.

The capacitance changeover circuit 600 is formed from a plurality ofparallel connections of series circuits wherein a capacitor is connectedbetween the source of a MOSFET which forms a switch circuit and theconnecting point P1 and between the drain of the MOSFET and theconnecting point P2.

In particular, capacitors 621, 622, . . . , 62 n are connected betweenthe sources MOSFETs 611, 612, . . . , 61 n and the connecting point P1,respectively, and capacitors 631, 632, . . . , 63 n are connectedbetween the drains of the MOSFETs 611, 612, . . . , 61 n and theconnecting point P2, respectively.

The controlling signal generation section 700 supplies a switchingcontrolling signal SW for on/off switching to the gate of the MOSFETs611, 612, . . . , 61 n.

In the VCO having the configuration described above, if any of theMOSFETs 611, 612, . . . , 61 n is turned on by the switching controlsignal SW, then the capacitors connected on the opposite sides of theMOSFET are connected in series between the connecting point P1 and theconnecting point P2.

Accordingly, the series circuits of the capacitors connected to theopposite sides only of those ones of the MOSFETs 611, 612, . . . , 61 nwhich are controlled to an on state by the switching control signal areconnected in parallel to the variable capacitance circuit 110. In otherwords, the number of series circuits of the capacitors connected inparallel between the connecting point P1 and the connecting point P2 isvaried in response to the switching controlling signal SW to the MOSFETs611, 612, . . . , 61 n.

Consequently, the oscillation center frequency of the VCO is controlledto shift in response to the switching controlling signal SW to theMOSFETs 611, 612, . . . , 61 n.

In the VCO of the third embodiment, the controlling signal generationsection 700 produces the controlling signals VR1 and VR2 so thatvariation control of the resistance value of the variable resistancecircuits 400 and 500 is carried out in response to the shift control ofthe oscillation center frequency of the VCO in addition to the operationof the VCO of the second embodiment described hereinabove.

In the VCO of the third embodiment having the configuration describedabove, even when the variation frequency range of the VCO is shifted,the resistance value of the variable resistance circuits 400 and 500 iscontrolled in response to the shift, and consequently, the oscillationamplitude of the oscillation output signal from the VCO does notdeteriorate. In other words, the oscillation amplitude of theoscillation output signal from the VCO can normally be keptsubstantially fixed within the overall variation frequency range forshifting.

It is to be noted that the VCO shown in FIG. 6 uses the variableresistance circuits 400 and 500 used in the VCO shown in FIG. 4.However, also in the VCO of the third embodiment, the variableresistance circuits 400 and 500 can be formed, for example, from avariable resistance element for which a MOSFET is used or from acombination of a resistance element and a switch circuit. Also it ispossible for the variable resistance circuits 400 and 500 to use, forexample, both of a variable resistance element for which a MOSFET isused and a combination of a resistance element and a switch circuit.

Fourth Embodiment

The fourth embodiment is an example wherein a VCO according to anembodiment is used as a variable frequency oscillation circuit of a PLLcircuit of a tuner section or front end circuit of a televisionbroadcasting signal receiving apparatus. In the present fourthembodiment, the front end circuit is formed as a one-chip IC.

As regards an IC circuit, where an internal component circuit includes aresistance element, the resistance element exhibits a dispersion foreach IC. Therefore, preferably the VCO, for example, of the thirdembodiment described above is configured such that the resistors 421,422, . . . , 42 n of the variable resistance circuit 400 and theresistors 521, 522, . . . , 52 n of the variable resistance circuit 500can be adjusted against the dispersion for each IC.

Dispersion adjustment data for a VCO or some other circuit section whichuses a resistance element for each front end circuit IC can be acquiredbefore shipment from a factory, for example, using a tester. In thepresent fourth embodiment, a nonvolatile memory for storing suchadjustment data is built in a front end circuit IC in advance, andadjustment data acquired using the tester described above are storedinto the nonvolatile memory so that adjustment against a dispersion byresistance can be carried out.

Now, the fourth embodiment is described in detail.

FIG. 7 shows an example of a configuration of part of a televisionbroadcast receiver to which the VCO of the fourth embodiment is applied.Referring to FIG. 7, the television broadcast receiver has a simplifiedconfiguration thanks to adoption of ICs and includes a front end circuitIC 1 and a demodulation circuit IC 2 as principal components thereof andfurther includes a system controller 4 formed including a microcomputer.Further, the demodulation circuit IC 2 includes a signal processor 61formed from a microcomputer.

A remote control signal reception section 8 is connected to the systemcontroller 4. The remote control signal reception section 8 receives aremote control signal from a remote control signal transmitter 9 andtransfers the remote control signal to the system controller 4. Thesystem controller 4 analyzes the received remote control signal, decidesa user operation such as a power on/off operation or a channel selectionoperation, and carries out suitable control in response to a result ofthe decision.

A television broadcast signal received by a television broadcast signalreception antenna 5 is supplied to the front end circuit IC 1 through anantenna terminal pin T11.

In the present embodiment, the front end circuit IC 1 includes a frontend circuit section 10 which is an example of an internal componentwhich can be adjusted with adjustment data, a nonvolatile memory 51 forstoring adjustment data acquired in advance, and an interface section52.

The front end circuit section 10 includes a PLL circuit which includesthe VCO according to the present embodiment and a plurality ofadjustment requiring portions which require adjustment thereof against adispersion. Adjustment data determined in advance regarding adjustmentitems of the adjustment requiring portions of the front end circuitsection 10 before shipment of the television broadcast receiver from afabrication factory are stored as beforehand acquired adjustment data inthe nonvolatile memory 51.

The nonvolatile memory 51 is connected to the interface section 52. Theinterface section 52 is connected to a signal processor or microcomputer61 hereinafter described of the demodulation circuit IC 2 through aterminal pin T14 of the front end circuit IC 1.

In this instance, in order to acquire beforehand acquired adjustmentdata, the tester is used to first adjust the adjustment data regardingthe adjustment items of the adjustment requiring portions so that anoptimum state may be obtained at a value determined in advance of aparameter which varies, in the present embodiment, of the frequency of achannel to be selected. Then, the adjustment data when the optimum stateis obtained are stored as the beforehand acquired adjustment data in acorresponding relationship to the corresponding parameter value, thatis, the corresponding frequency value, into the nonvolatile memory 51through the signal processor 61.

It is to be noted that alternatively the tester may write the beforehandacquired adjustment data not through the signal processor 61 but throughthe interface section 52.

In the present embodiment, as regards the parameter values at which thebeforehand acquired adjustment data are stored, the beforehand acquiredadjustment data need not be acquired for the frequencies correspondingto all channels to be selected but may be discrete parameter values. Ashereinafter described, adjustment data corresponding to a parametervalue between the discrete parameter values can be acquired by aninterpolation process from the beforehand acquired adjustment datastored in the nonvolatile memory as hereinafter described.

For example, where the dispersion of the above-described resistance ofthe VCO varies in response to the variation of the oscillation frequencyof the VCO, there is no necessity to store a great number of data of allreceiving channel frequencies and so forth, but adjustment data atdiscrete receiving channel frequencies are stored. Alternatively, wherethe dispersion of the resistance of the VCO does not depend upon theoscillation frequency of the VCO, there is no necessity to store a largenumber of data of all receiving channel frequencies and so forth, but acertain one adjustment data is stored.

It is to be noted that the formerly acquired data stored in thenonvolatile memory 51 are in an error correction encoded form.

Some of the beforehand acquired adjustment data stored in thenonvolatile memory 51 which do not exhibit any variation with regard toa parameter such as the frequency may be supplied as they are as actualadjustment data to the adjustment requiring portions of the front endcircuit section 10 if they are subjected to an error correction decodingprocess.

However, as regards principal adjustment data where the channelfrequency is a parameter, if it is tried to store the data for allparameter values, then a large number of data is to be stored asdescribed hereinabove. Therefore, a comparatively small number ofbeforehand acquired adjustment data only for discrete parameter valuesare stored. Accordingly, in this instance, the beforehand acquiredadjustment data are not actual adjustment data which are supplied asthey are to the adjustment requiring portions of the front end circuitsection 10, but are used as basic data when the signal processor ormicrocomputer 61 of the demodulation circuit IC 2 hereinafter describedproduces actual adjustment data by an interpolation process.

The beforehand acquired adjustment data stored in the nonvolatile memory51 are read out in accordance with a reading out request received fromthe signal processor 61 of the demodulation circuit IC 2 through theinterface section 52. The interface section 52 has a function oftransferring the beforehand acquired adjustment data read out from thenonvolatile memory 51 in accordance with the reading out request to thesignal processor 61.

As hereafter described, the signal processor 61 produces actual useadjustment data from the beforehand acquired adjustment data read outfrom the nonvolatile memory 51 and sends the actual use adjustment datato the front end circuit IC 1. The interface section 52 has a functionof receiving the actual use adjustment data from the signal processor61, storing the actual use adjustment data into the built-in registerand supplying the actual use adjustment data to the adjustment requiringportions of the front end circuit section 10.

The front end circuit section 10 converts a received televisionbroadcast signal into an intermediate frequency signal. Then, the frontend circuit section 10 signals the intermediate frequency signal to thedemodulation circuit IC 2 through a terminal pin T12.

In the present embodiment, the demodulation circuit IC 2 includes ademodulation circuit section 60 for producing an image output signalfrom the intermediate frequency signal and the signal processor ormicrocomputer 61 described hereinabove.

To the demodulation circuit section 60, the intermediate frequencysignal from the front end circuit IC 1 is supplied through a terminalpin T21. The demodulation circuit section 60 demodulates the inputtedintermediate frequency signal to produce an image output signal andsupplies the image output signal to an image output amplifier through aterminal pin T22.

The signal processor 61 is connected to the interface section 52 of thefront end circuit IC 1 through a terminal pin T23 and connected also tothe system controller 4 through a terminal pin T24.

The signal processor 61 has a function of carrying out writing/readingout accessing to the nonvolatile memory 51 and a function of errorcorrecting and decoding the beforehand acquired adjustment data acquiredfrom the nonvolatile memory 51 to produce actual use adjustment data.The function of producing actual use adjustment data includes a functionof producing actual use adjustment data from beforehand acquiredadjustment data by interpolation.

Particular Example of the Front End Circuit IC 1

FIG. 8 shows a particular example of the front end circuit IC 1 in thepresent embodiment, particularly of the front end circuit section 10.

Various frequencies or channels are used for television broadcasting indifferent countries, and the NTSC (National Television System Committee)system, the PAL (Phase Alternating Line) system, the SECAM (Séquentielcouleur à mémoire) system and so forth are available as the colortelevision system. Further, also analog broadcasts and digitalbroadcasts are available.

Therefore, it seems a promising countermeasure to divide the receptionsignal system for a television broadcast into a front end circuit forreceiving a television broadcast and outputting an intermediatefrequency signal and a base band processing circuit for processing theoutput of the front end circuit and outputting a color image signal anda sound signal. The countermeasure deals with the difference in thebroadcasting system of a television broadcast.

FIG. 8 shows an example of a front end circuit configured to receivetelevision broadcasts in various countries irrespective of thedifference in the broadcasting form. The front end circuit of FIG. 8divides the frequencies used in television broadcasts in differentcountries into three bands including

-   -   (A) 46 to 147 MHz (VHV-L band),    -   (B) 147 to 401 MHz (VHF-H band), and    -   (C) 401 to 887 MHz (UHF band)        such that the frequency to be used can be changed in accordance        with an object channel in each of the reception bands.

Referring to FIG. 8, a block 1 surrounded by a chain line denotes thefront end circuit which is formed as an one-chip IC as describedhereinabove.

Broadcasting wave signals of television broadcasts are received by anantenna, and reception signals of the received broadcasting wave signalsare selectively supplied to antenna tuning circuits 12A to 12C through aswitch circuit 11 past the terminal pin T11. In this instance, theantenna tuning circuits 12A to 12C correspond to the reception bands of(A) to (C) given hereinabove, respectively. Each of the antenna tuningcircuits 12A to 12C changes with digital data the capacitance of atuning capacitor to change the tuning frequency so as to be tuned to thereception signal of an object frequency or channel.

The reception signals from the antenna tuning circuits 12A to 12C aresupplied to a switch circuit 15 through high frequency amplificationcircuits 13A to 13C and then through interstage tuning circuits 14A to14C, respectively. The switch circuit 15 is switched in an interlockingrelationship with the switch circuit 11, and accordingly, a receptionsignal SRX of an object reception band is extracted from the switchcircuit 15. Then, the extracted reception signal SRX is supplied tomixer circuits 21I and 21Q.

It is to be noted that, although also the interstage tuning circuits 14Ato 14C are formed similarly to the antenna tuning circuits 12A to 12C,the interstage tuning circuit 14A is formed as a demodulation tuningcircuit. Further, as hereinafter described, the tuning capacitors of thetuning circuits 12A to 12C and 14A to 14C are built in the IC 1, but thetuning coils are provided externally of the IC 1.

A VCO 31 has a configuration to which the VCO of the third embodiment isapplied. The VCO 31 forms an oscillation signal of a predeterminedfrequency. The VCO 31 is used to form a local oscillation signal andforms part of a PLL circuit 30. In particular, the oscillation signal ofthe VCO 31 is supplied to a variable dividing circuit 32, by which it isdivided into a signal of a 1/N (N is a positive integer) frequency. Thedivided signal is supplied to a phase comparison circuit 33. Further, aclock having a frequency of about 1 to 2 MHz is supplied to a signalformation circuit 34 through a terminal pin T16 to be divided into asignal of a predetermined frequency f34. The divided signal is suppliedas a reference signal to a phase comparison circuit 33.

Then, a comparison output of the phase comparison circuit 33 is suppliedto a loop filter 35, from which a dc voltage, that is, a controllingvoltage VC, whose level varies in response to the phase differencebetween the output signal of the variable dividing circuit 32 and anoutput signal of the signal formation circuit 34. The dc voltage, thatis, the controlling voltage VC, is supplied as a control voltage for theoscillation frequency f31 to the VCO 31. It is to be noted that asmoothing capacitor C11 is externally connected to the loop filter 35through a terminal pin T17.

Accordingly, the oscillation frequency f31 of the VCO 31 is given byf31=N·f34  (expression 2)

Therefore, the oscillation frequency f31 of the VCO 31 can be changed bythe system controller 4 by controlling the dividing ratio N through thesignal processor 61. For example, the oscillation frequency f31 is 1.8to 3.6 GHz in response to the reception band and the reception frequencyor reception channel.

Then, the oscillation signal of the VCO 31 is supplied to a variabledividing circuit 36, by which it is divided into a frequency of 1/M (forexample, M=2, 4, 8, 16 or 32). Also the dividing ratio M of the variabledividing circuit 36 is controlled through the signal processor 61 by thesystem controller 4.

Then, the divided signal from the variable dividing circuit 36 issupplied to a dividing circuit 37, by which it is divided into dividingsignals SL0I and SL0Q which have a ½ frequency and have phasesorthogonal to each other. The dividing signals SL0I and SL0Q aresupplied as local oscillation signals to the mixer circuits 21I and 21Q,respectively.

Here, if

fL0: frequency of the dividing signals SL0I and SL0Q

then

$\begin{matrix}{{{fL}\; 0} = {f\;{31/\left( {2M} \right)}}} \\{= {{N \cdot f}\;{34/\left( {2M} \right)}}} \\{= {f\;{34 \cdot {N/\left( {2M} \right)}}}}\end{matrix}$Accordingly, by changing the dividing ratios M and N, the localoscillation frequency fL0 can be varied with a predetermined frequencystep over a wide range.

Further,

SRX: reception signal to be received

SUD: image disturbance signal

and, for the simplification,SRX=ERX·sin ωRXt

-   -   ERX: amplitude of the reception signal SRX    -   ωRX=2πfRX    -   fRX: center frequency of the reception signal SRX        SUX=EUD·sin ωUDt    -   EUD: amplitude of the image disturbance signal SUD    -   ωUD=2πfUD    -   fUD: center frequency of the image disturbance signal SUD

Further, the local oscillation signals SL0I and SL0Q are set asSL0I=EL0·sin ωL0tSL0Q=EL0·cos ωL0t

-   -   EL0: amplitude of the signals SL0I and SL0Q    -   ωL0=2πfL0

However, in this instance, ifωIF=2πfIF

-   -   fIF: intermediate frequency. For example, 4 to 5.5 MHz (varied        depending upon the broadcasting system)        then, in the case of the upper heterodyne system,        fRX=fL0−fIF        fUD=fL0+fIF

Accordingly, the mixer circuits 21I and 21Q output the following signalsSIFI and SIFQ, respectively. In particular, the signals SIFI and SIFQ of

$\begin{matrix}{{SIFI} = {\left( {{SRX} + {SUD}} \right) \times {SL}\; 0I}} \\{= {{{{ERX} \cdot \sin}\;\omega\;{RXt} \times {EL}\;{0 \cdot \sin}\;\omega\; L\; 0t} +}} \\{{{EUD} \cdot \sin}\;\omega\;{UDt} \times {EL}\;{0 \cdot \sin}\;\omega\; L\; 0t} \\{= {{\alpha\left\{ {{{\cos\left( {{\omega\;{RX}} - {\omega\; L\; 0}} \right)}t} - {{\cos\left( {{\omega\;{RX}} + {\omega\; L\; 0}} \right)}t}} \right\}} +}} \\{\beta\left\{ {{{\cos\left( {{\omega\;{UD}} - {\omega\; L\; 0}} \right)}t} - {{\cos\left( {{\omega\;{UD}} + {\omega\; L\; 0}} \right)}t}} \right\}}\end{matrix}$ $\begin{matrix}{{SIFQ} = {\left( {{SRX} + {SUD}} \right) \times {SL}\; 0Q}} \\{= {{{{ERX} \cdot \sin}\;\omega\;{RXt} \times {EL}\;{0 \cdot \cos}\;\omega\; L\; 0t} +}} \\{{{EUD} \cdot \sin}\;\omega\;{UDt} \times {EL}\;{0 \cdot \cos}\;\omega\; L\; 0t} \\{= {{\alpha\left\{ {{{\sin\left( {{\omega\;{RX}} + {\omega\; L\; 0}} \right)}t} + {{\sin\left( {{\omega\;{RX}} - {\omega\; L\; 0}} \right)}t}} \right\}} +}} \\{\beta\left\{ {{{\sin\left( {{\omega\;{UD}} + {\omega\; L\; 0}} \right)}t} + {{\sin\left( {{\omega\;{UD}} - {\omega\; L\; 0}} \right)}t}} \right\}}\end{matrix}$ α = ERX ⋅ EL 0/2 β = EUD ⋅ EL 0/2are extracted.

Then, the signals SIFI and SIFQ are supplied to a low-pass filter 22having a greater bandwidth than the occupation bandwidth, which is, forexample, 6 to 8 MHz, of an image intermediate frequency signal and asound intermediate frequency signal. As a result, the low-pass filter 22removes signal components of the sum angular frequencies (ωRX+ωL0) and(ωUD+ωL0) (and the local oscillation signals SL0I and SL0Q).Consequently,

$\begin{matrix}\begin{matrix}{{SIFI} = {{{\alpha \cdot {\cos\left( {{\omega\;{RX}} - {\omega\; L\; 0}} \right)}}t} + {{\beta \cdot {\cos\left( {{\omega\;{UD}} - {\omega\; L\; 0}} \right)}}t}}} \\{= {{{\alpha \cdot \cos}\;\omega\;{IFt}} + {{\beta \cdot \cos}\;\omega\;{IFt}}}}\end{matrix} & \left( {{expression}\mspace{14mu} 4} \right) \\\begin{matrix}{{SIFQ} = {{{\alpha \cdot {\sin\left( {{\omega\;{RX}} - {\omega\; L\; 0}} \right)}}t} + {{\beta \cdot {\sin\left( {{\omega\;{UD}} - {\omega\; L\; 0}} \right)}}t}}} \\{= {{{{- \alpha} \cdot \sin}\;\omega\;{IFt}} + {{\beta \cdot \sin}\;\omega\;{IFt}}}}\end{matrix} & \left( {{expression}\mspace{14mu} 5} \right)\end{matrix}$are extracted from the low-pass filter 22.

Then, the signals SIFI and SIFQ are supplied to a complex band-passfilter 24, which is a polyphase band-pass filter, through a amplitudephase correction circuit 23 hereinafter described. The complex band-passfilter 24 has the following characteristics (a) to (d):

(a) It has a frequency characteristic of a band-pass filter.

(b) It has a phase shift characteristic and shifts the phase of thesignal SIFI by a value φ which is an arbitrary value.

(c) It shifts the phase of the signal SIFQ by a value (φ−90°) similarly.

(d) It has two band-pass characteristics which have a frequency f0 andanother frequency −f0, which are symmetrical with respect to the zerofrequency on a frequency axis, as the center frequencies thereof, andone of the two band-pass characteristics can be selected by a relativephase between the input signals.

Accordingly, the complex band-pass filter 24 delays the signal SIFQ by90° with respect to the signal SIFI from the items (b) and (c) above asgiven by

$\begin{matrix}{{SIFI} = {{{\alpha \cdot \cos}\;\omega\;{IFt}} + {{\beta \cdot \cos}\;\omega\;{IFt}}}} & \left( {{expression}\mspace{14mu} 6} \right) \\\begin{matrix}{{SIFQ} = {{{- \alpha} \cdot {\sin\left( {{\omega\;{IFt}} - {90{^\circ}}} \right)}} + {\beta \cdot {\sin\left( {{\omega\;{IFt}} - {90{^\circ}}} \right)}}}} \\{= {{{\alpha \cdot \cos}\;\omega\;{IFt}} - {{\beta \cdot {coc}}\;\omega\;{IFt}}}}\end{matrix} & \left( {{expression}\mspace{14mu} 7} \right)\end{matrix}$

In short, in the signal SIFI and the signal SIFQ, the signal componentsα·cos ωIFt have the same phase with each other whereas the signalcomponents β·cos ωIFt have phases opposite to each other.

Then, the signals SIFI and SIFQ are supplied to an level correctionamplifier 25 for level correction, by which they are added to eachother. Consequently, such a signal SIF as described below is extractedfrom the level correction amplifier 25.

In particular,

$\begin{matrix}\begin{matrix}{{SIF} = {{SIFI} + {SIFQ}}} \\{= {2\;{\alpha \cdot \cos}\;\omega\;{IFt}}} \\{= {{{ERX} \cdot {EL}}\;{0 \cdot \cos}\;\omega\;{IFt}}}\end{matrix} & \left( {{expression}\mspace{14mu} 8} \right)\end{matrix}$is extracted. The extracted signal SIF is nothing but an intermediatefrequency signal when the reception signal SRX is received in accordancewith the upper heterodyne system. This intermediate frequency signal SIFdoes not include the image disturbance signal SUD. It is to be notedthat the amplitude phase correction circuit 23 corrects the amplitudeand the phase of the signals SIFI and SIFQ so that the (expression 8)may be satisfied sufficiently, that is, the image disturbance signal SUDmay be minimized.

Further, at this time, the level correction amplifier 25 for levelcorrection corrects the level of the signal SIF so that, even if thelevel of the signals SIFI and SIFQ differs depending upon thebroadcasting system, an AGC characteristic hereinafter described,particularly the start level of AGC, or the like may not vary.

Then, the intermediate frequency signal SIF is outputted to the terminalpin T12 through a variable gain amplifier 26 for AGC and a band-passfilter 27 for dc component cutting and aliasing.

Accordingly, if the dividing ratios M and N are varied, then an objectfrequency or channel can be selected in accordance with the (expression3), and if the intermediate frequency signal SIF outputted to theterminal pin T12 is demodulated in accordance with the broadcastingsystem, then the object broadcast can be enjoyed.

In this manner, with the present front end circuit section 10, the broadfrequency range from 46 to 887 MHz can be coped with by a one-chip IC.Further, the front end circuit section 10 can be implemented using areduced number of parts without deteriorating the characteristic againstdisturbance over the wide frequency range. Further, the front endcircuit section 10 can cope with a difference in the broadcasting systembetween the analog broadcasting and the digital broadcasting or with adifference in the broadcasting system among different districts in theworld.

Further, reception disturbance by harmonics of a clock signal isreduced, and as a result, the reception sensitivity is improved.Furthermore, since all circuit components of the PLL circuit 30 exceptthe capacitor C11 can be formed on a chip, the PLL circuit 30 is toughagainst disturbance and suffers less likely from disturbance. Further,since only the interstage tuning circuits 14A to 14C are connected tothe high frequency amplification circuits 13A to 13C, respectively, theload is light and signal distortion by the high frequency amplificationcircuits 13A to 13C is low.

An AGC voltage VAGC is formed by an AGC voltage generation circuit 63 ofthe demodulation circuit IC 2 at the next stage to the front end circuitIC 1 and is supplied as a gain controlling signal to the variable gainamplifier 26 for AGC through a terminal pin T13. Accordingly, ordinaryAGC, that is, AGC of the intermediate frequency signal, is carried outwith the gain controlling signal.

Further, for example, if the level of the object reception signal SRX isexcessively high or a disturbance wave signal of a high level isincluded in the reception signal SRX, then the ordinary AGC cannot copewith this. Therefore, the signals SIFI and SIFQ outputted from thelow-pass filter 22 are supplied to a level detection circuit 41, bywhich it is detected whether or not the level of the signals SIFI andSIFQ before AGC is carried out by the amplifier 26 for AGC exceeds apredetermined value. Then, a detection signal of the level detectioncircuit 41 and the AGC voltage VAGC of the terminal pin T15 are suppliedto an addition circuit 42, and an addition output from the additioncircuit 42 is supplied to a delayed AGC voltage formation circuit 43, bywhich a delayed AGC voltage VDAGC is formed. The delayed AGC voltageVDAGC is supplied as a gain controlling signal to the high frequencyamplification circuits 13A to 13C to carry out delay AGC.

Accordingly, since optimum AGC operation can be achieved from D/U of theintensity of a signal to be received and the intensity of many signalsnot to be received, a desired broadcast from among digital broadcasts,analog broadcasts or digital and analog broadcast can be receivedfavorably.

The signals SIFI and SIFQ outputted from the low-pass filter 22 aresupplied to a linear detection circuit 44, by which they are detectedand smoothed to form a dc voltage V44 which represents the level of thesignals SIFI and SIFQ. The dc voltage V44 is outputted to a terminal pinT15.

The dc voltage V44 outputted to the terminal pin T15 is used upontesting or adjustment of the front end circuit IC 1. For example, the dcvoltage V44 can be used in order to check the level of the input signal,that is, the reception signal, over a wide frequency range. Inparticular, different from an output from an intermediate frequencyfilter of a narrow band, the attenuation characteristic over a wide bandalong the signal lines from the antenna terminal pin T11 to the mixercircuits 21I and 21Q can be checked directly.

Further, where the antenna tuning circuits 12A to 12C and the interstagetuning circuits 14A to 14C are to be adjusted, if a test signal isapplied to the antenna terminal pin T11 and the AGC voltage VAGC to besupplied to the terminal pin T13 is fixed to a predetermined value, thentracking adjustment can be carried out from the variation of the dcvoltage V44. Further, adjustment of various functions and measurement ofa characteristic of the front end circuit IC 1 can be carried out withdigital data, and automatic adjustment and automatic measurement can becarried out.

Constant Voltage Circuit

The front end circuit IC 1 in the present embodiment includes a constantvoltage circuit 53, to which a power supply voltage +VCC is suppliedthrough a terminal pin T18. The constant voltage circuit 53 makes use ofa band gap of the PN junction to form a constant voltage of apredetermined value from the power supply voltage +VCC, and the constantvoltage formed in this manner is supplied to the component circuits ofthe IC 1. It is to be noted that an output voltage of the constantvoltage circuit 53 can be adjusted finely, and adjustment data thereforis stored in the nonvolatile memory 51. The signal processor 61 acquiresthe adjustment data for fine adjustment from the nonvolatile memory 51to produce actual use adjustment data and supplies the actual useadjustment data to the constant voltage circuit 53 through the interfacesection 52.

Accordingly, the output power supply voltage of the constant voltagecircuit 53 is a constant voltage finely adjusted for each front endcircuit IC 1. Therefore, even where the component circuits are formedfrom MOSFETs, the power supply voltage to be supplied to the circuitscan be set to a rather high value. Consequently, the performance of theMOSFETs can be extracted in the maximum.

With the configuration of the front end circuit IC 1 shown in FIG. 8,television broadcasts in the frequency band of 46 to 887 MHz asindicated in the items (A) to (C) given hereinabove. At this time, sincethe center frequency and the pass-band width of the complex band-passfilter 24 are variable, not only ground wave digital televisionbroadcasts and ground wave analog television broadcasts in Japan butalso those outside Japan can be coped with.

FIG. 9 shows a more detailed configuration of the control section of theVCO 31 in the fourth embodiment.

In the present embodiment, for example, if a power supply is madeavailable to the broadcast receiver, then the signal processor 61 sendsan acquisition request for beforehand acquired adjustment data to thenonvolatile memory 51 through the interface section 52 to read out thebeforehand acquired adjustment data from the nonvolatile memory 51.Then, the signal processor 61 receives the beforehand acquiredadjustment data read out from the nonvolatile memory 51 through theinterface section 52 and stores the received beforehand acquiredadjustment data into a cache memory built therein. At this time, thesignal processor 61 carries out an error correction decoding process forthe read out adjustment data.

During operation wherein the power supply is on, the signal processor 61uses the beforehand acquired adjustment data stored in the cache memoryto produce actual use adjustment data. Thereupon the signal processor 61carries out also a process of producing actual use adjustment datathrough an interpolation process based on the beforehand acquiredadjustment data stored in the cache memory.

Then, the signal processor 61 supplies the produced actual useadjustment data to the VCO 31 and the individual adjustment objectportions of the front end circuit section 10 through the interfacesection 52.

As seen in FIG. 9, the interface section 52 supplies, from among thereceived actual use adjustment data, adjustment data VR1 and VR2 for theVCO 31 to the variable resistance circuit 400 and the variableresistance circuit 500, respectively, so that the resistance is adjustedagainst a dispersion and the bias current value to the variablecapacitance circuit 110 is controlled to prevent deterioration of theoscillation amplitude of the oscillation output signal from the VCO 31.Further, the interface section 52 supplies the switching controllingsignal SW received from the signal processor 61 to the capacitancechangeover circuit 600 to change over the oscillation center frequency.

With the present fourth embodiment, the resistance value of the variableresistance circuit 400 and the variable resistance circuit 500 can befinely adjusted using dispersion adjustment data determined in advance.

It is to be noted that, as seen in FIG. 9, in the present fourthembodiment, the power supply potential VDD of the VCO 31 is a potentialformed as a constant voltage by the constant voltage circuit 53 in thefront end circuit IC 1.

Although the spurious characteristic or the phase noise characteristicof a VCO is sometimes influenced much by external noise or thermal noisemixed into a power supply voltage, in the present embodiment, since thepower supply potential VDD is formed as a constant voltage by theconstant voltage circuit 53, the problem described is moderated. In thisinstance, the constant voltage circuit 53 preferably has a low outputnoise characteristic and a high power supply rejection ratio (PSRR)characteristic so that the influence of external noise and so forth canbe reduced.

It is to be noted that, as described hereinabove, the configuration ofthe variable resistance circuits 400 and 500 is not limited to thatdescribed hereinabove with reference to FIG. 6 which is composed of aswitch circuit and a resistance element, but a MOSFET may be used as avariable resistance element, or both of a variable resistance circuitwhich uses a MOSFET as a variable resistance element and anothervariable resistance circuit which uses a switch circuit and a resistanceelement as a variable resistance element may be used. Where a MOSFET isused as a variable resistance element, fine adjustment of the resistancevalue is easy.

Fifth Embodiment

An example of a configuration of a VCO according to a fifth embodimentis shown in FIG. 10. Referring to FIG. 10, in the VCO of the presentfifth embodiment, an oscillation amplitude of the VCO obtained betweenthe connecting point P1 and the connecting point P2, that is, betweenthe drain of the MOSFET 121 and the drain of the MOSFET 122, is detectedby an amplitude detector 801. Then, the value of the oscillationamplitude of the VCO detected by the amplitude detector 801 is suppliedto a control section 802.

The control section 802 controls the variable resistance circuits 400and 500 so that the detection oscillation amplitude may be fixed.

Consequently, with the present fifth embodiment, characteristicdeterioration of the VCO arising from a dispersion in the oscillationfrequency or a resistance element can be compensated for.

Sixth Embodiment

An example of a configuration of a VCO according to a sixth embodimentis shown in FIG. 11. In the first embodiment, the negative resistancecircuit 102 is formed from the MOSFETs 121 and 122 as seen in FIG. 1. Incontrast, in the present sixth embodiment, the negative resistancecircuit 102 is composed of a pair of P-type MOSFETs 123 and 124.

In the present sixth embodiment, a connecting point of the sources ofthe P-type MOSFETs 123 and 124 which have a differential configurationtherebetween is connected to the power supply line 104 through the firstresistor 301 similarly to that of the MOSFETs 121 and 122. A connectingpoint of the coils L1 and L2 of the resonance circuit 101 is groundedthrough the second resistor 302.

Seventh Embodiment

An example of a configuration of a VCO of a seventh embodiment is shownin FIG. 12.

In the present seventh embodiment, the negative resistance circuit isformed in a CMOS configuration including a negative resistance circuit102A formed from a pair of N-type MOSFETs 121 and 122 and anothernegative resistance circuit 102B formed from a pair of P-type MOSFETs123 and 124.

Referring to FIG. 12, in the present seventh embodiment, a connectingpoint of the sources of the P-type MOSFETs 123 and 124 of the negativeresistance circuit 102B is connected to the power supply line 104through the resistor 301. Meanwhile, a connecting point of the sourcesof the MOSFETs 121 and 122 of the negative resistance circuit 102A isgrounded through the resistor 302.

The resonance circuit 101 including the variable capacitance circuit 110is provided between the negative resistance circuit 102A and thenegative resistance circuit 102B.

Eighth Embodiment

In the first to seventh embodiments described above, the first resistor301 is connected between the oscillation circuit section 103 and one ofthe terminals of the power supply and the second resistor 302 isconnected also between the oscillation circuit section 103 and the otherterminal of the power supply.

However, from the object of increasing the variable capacitance regionfrom an existing one by adjusting the bias voltage to a variablecapacitance element which composes a variable capacitance circuit, acurrent supply source may be connected in place of the second resistor302.

FIG. 13 shows an example of the eighth embodiment which has theconfiguration just described. In particular, the VCO is a modificationto but is different from the VCO of the first embodiment in that acurrent source 303 is provided in place of the second resistor 302.

Other Embodiments and Modifications

While, in the embodiments described above, a varactor is used as avariable capacitance element of the current controlled type, thevariable capacitance element to which the present application is appliedis not limited to the varactor.

Further, while, in the foregoing description, only a case is describedwherein the voltage-controlled variable frequency oscillation circuitaccording to the present application is used only as a VCO of a PLLcircuit of a front end circuit of a television broadcast receiver, theapplication of the VCO of the present application is not limited tothis, but the VCO can be applied to various signal processing circuits.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A voltage-controlled variable frequency oscillation circuit,comprising: an oscillation circuit section including a resonance circuitwhich includes a coil and a variable capacitance element, and a negativeresistance circuit; and a first resistor connected between the resonancecircuit of said oscillation circuit section and a first one of a pair ofterminals of a power supply, wherein said first resistor includes aplurality of resistance elements and a plurality of switch circuits,said switch circuits being individually controlled with a controllingsignal between on and off to variably control the resistance value ofsaid first resistor ; a second resistor connected between the negativeresistance circuit of said oscillation circuit section and a second oneof the terminals of the power supply, wherein both of said firstresistor and said second resistor have a variably controllableresistance value, and wherein both of said first resistor and saidsecond resistor are formed from a plurality of resistance elements and aplurality of switch circuits, and said switch circuits are individuallycontrolled between on and off to variably control the resistance valueof said first and second resistors.
 2. The voltage-controlled variablefrequency oscillation circuit according to claim 1, wherein saidresonance circuit includes a variable capacitance circuit whosecapacitance is variably controlled in accordance with an oscillationfrequency, and the resistance value of said first resistance is variedin response to the variation control of the capacitance in accordancewith the oscillation frequency.
 3. The voltage-controlled variablefrequency oscillation circuit according to claim 1, further comprising adetection circuit for detecting the amplitude of an oscillation outputsignal of said oscillation circuit section and variably controlling theresistance value of said first resistor.
 4. The voltage-controlledvariable frequency oscillation circuit according to claim 1, whereinboth of said first resistor and said second resistor are formed from avariable resistance element whose resistance value is variablycontrolled with a controlling signal.
 5. The voltage-controlled variablefrequency oscillation circuit according to claim 1, wherein the powersupply provides a fixed voltage formed by a constant voltage circuit. 6.The voltage-controlled variable frequency oscillation circuit accordingto claim 2, wherein the resonance circuit further includes a capacitancechangeover circuit for shifting an oscillation center frequency.
 7. Thevoltage-controlled variable frequency oscillation circuit according toclaim 6, wherein the resonance circuit further includes a plurality ofcoils, and wherein the capacitance changeover circuit is connected inparallel to the variable capacitance circuit between the variablecapacitance circuit and the plurality of coils.
 8. Thevoltage-controlled variable frequency oscillation circuit according toclaim 7, wherein the capacitance changeover circuit includes at leastone switch circuit connected between two capacitors.
 9. Avoltage-controlled variable frequency oscillation circuit, comprising:an oscillation circuit section including a resonance circuit whichincludes a coil and a variable capacitance element, and a negativeresistance circuit, a first resistor connected between the resonancecircuit of said oscillation circuit section and a first one of a pair ofterminals of a power supply, wherein said first resistor includes aplurality of resistance elements and a plurality of switch circuits,said switch circuits being individually controlled with a controllingsignal between on and off to variably control the resistance value ofsaid first resistor, a second resistor connected between the negativeresistance circuit of said oscillation circuit section and a second oneof the terminals of the power supply, wherein both of said firstresistor and said second resistor have a variably controllableresistance value, wherein said resonance circuit includes a variablecapacitance circuit whose capacitance is variably controlled inaccordance with an oscillation frequency, and the resistance value ofboth of said first and second resistors is varied in response tovariation control of the capacitance in accordance with the oscillationfrequency.
 10. A voltage-controlled variable frequency oscillationcircuit, comprising: an oscillation circuit section including aresonance circuit which includes a coil and a variable capacitanceelement, and a negative resistance circuit, a first resistor connectedbetween the resonance circuit of said oscillation circuit section and afirst one of a pair of terminals of a power supply, wherein said firstresistor includes a plurality of resistance elements and a plurality ofswitch circuits, said switch circuits being individually controlled witha controlling signal between on and off to variably control theresistance value of said first resistor, a second resistor connectedbetween the negative resistance circuit of said oscillation circuitsection and a second one of the terminals of the power supply, whereinboth of said first resistor and said second resistor have a variablycontrollable resistance value; and a detection circuit for detecting theamplitude of an oscillation output signal of said oscillation circuitsection and variably controlling the resistance value of both of saidfirst and second resistors.
 11. A signal processing circuit, comprising:a voltage-controlled variable frequency oscillation circuit including:an oscillation circuit section including a resonance circuit whichincludes a coil and a variable capacitance element and a negativeresistance circuit, (ii) a first resistor connected between saidoscillation circuit section and a first one of a pair of terminals of apower supply, (iii) a second resistor connected between said oscillationcircuit section and a second one of the terminals of the power supply;and a processing circuit configured to carry out a predetermined signalprocess using an oscillation frequency signal from saidvoltage-controlled variable frequency oscillation circuit, wherein bothof said first and second resistors have a resistance value which isvariably controlled with adjustment data, wherein both of said firstresistor and said second resistor are formed from a plurality ofresistance elements and a plurality of switch circuits, and said switchcircuits are individually controlled between on and off to variablycontrol the resistance value of said first and second resistors.
 12. Thesignal processing circuit according to claim 11, wherein said signalprocessing circuit further comprises: storage means for storingadjustment data for the dispersion of the resistance value of both ofsaid first and second resistors; and a circuit section configured tocontrol the resistance value of both of said first and second resistorsusing the adjustment data stored in said storage means.
 13. The signalprocessing circuit according to claim 12, wherein the power supply ofsaid voltage-controlled variable frequency oscillation circuit providesa fixed voltage formed by a constant voltage circuit.
 14. The signalprocessing circuit according to claim 11, wherein said signal processingcircuit is a phase-locked loop circuit.
 15. A signal processing circuit,comprising: a voltage-controlled variable frequency oscillation circuitincluding: an oscillation circuit section including a resonance circuitwhich includes a coil and a variable capacitance element and a negativeresistance circuit; (ii) a first resistor connected between saidoscillation circuit section and a first one of a pair of terminals of apower supply, wherein said first resistor includes a plurality ofresistance elements and a plurality of switch circuits, said switchcircuits being individually controlled with a controlling signal betweenon and off to variably control the resistance value of said firstresistor; (iii) a second resistor connected between said oscillationcircuit section and a second one of the terminals of the power supply;and a processing circuit configured to carry out a predetermined signalprocess using an oscillation frequency signal fom saidvoltage-controlled variable frequency oscillation circuit, wherein bothof said first and second resistors have a resistance value which isvariably controlled with adjustment data, wherein said resonance circuitincludes a variable capacitance circuit whose capacitance is variablycontrolled in accordance with an oscillation frequency, and wherein theresistance value of both of said first and second resistors is varied inresponse to variation control of the capacitance in accordance with theoscillation frequency.
 16. A signal processing circuit, comprising: avoltage-controlled variable frequency oscillation circuit including: anoscillation circuit section including a resonance circuit which includesa coil and a variable capacitance element and a negative resistancecircuit; (ii) a first resistor connected between said oscillationcircuit section and a first one of a pair of terminals of a powersupply, wherein said first resistor includes a plurality of resistanceelements and a plurality of switch circuits, said switch circuits beingindividually controlled with a controlling signal between on and off tovariably control the resistance value of said first resistor; (iii) asecond resistor connected between said oscillation circuit section and asecond one of the terminals of the power supply; and a processingcircuit configured to carry out a predetermined signal process using anoscillation frequency signal from said voltage-controlled variablefrequency oscillation circuit, wherein both of said first and secondresistors have a resistance value which is variably controlled withadjustment data; and a detection circuit for detecting the amplitude ofan oscillation output signal of said oscillation circuit section andvariably controlling the resistance value of both of said first andsecond resistors.